Several types of chemical analytical equipment utilize columns that are packed with a selectively absorbent packing material. An analyte is introduced into one end of the column, and a carrier fluid is then run through the column. The length of time that the analyte is retained within the column can enable identification of the analyte. Such techniques are used in liquid chromatography, high performance liquid chromatography, and ion exchange apparatus, among others. For example, in high performance liquid chromatography (HPLC), a column that is packed with a silica gel, a polystyrene gel, or an ion exchange resin may be used. The analyte is introduced into one end of the column, and a carrier fluid consisting of a mixture of two liquid solvents is flushed through the column. The ratio of solvents making up the carrier mixture is incrementally changed during the analysis.
Some chemical analytes may be irreversibly absorbed onto the packing material within an TPLC or other analvtical column. As material is irreversibly absorbed by the packing material, the column eventually begins to provide inaccurate results. Such contamination necessitates periodic repacking of the column with fresh packing material, or replacement with a new column.
In order to prolong the life of a column, a pre-column filter is often used upstream of the inlet of the analytical column. The pre-column filter conventionally consists of a short length of stainless steel tubing that is packed with the same packing material as is used in the column. Each end of the tubing is provided with a nut and ferrule in order to enable the pre-column filter assembly to be connected between the solvent/analyte source and the analytical column inlet. The expense of producing such a pre-column filter is not inconsequential because of the fittings and assembly required. When the pre-column filter becomes contaminated through use, it must either be repacked or discarded. When discarded, the fittings on the pre-column filter assembly are typically wasted.
Several different manufacturers' HPLC instruments are commonly used in laboratories. Often different instrument manufacturers use different styles of column inlet fittings on their instruments. For example, various instruments may include column fittings produced by: Parker Hannifin Corporation, Cleveland, Ohio; Waters Division of Millipore, Milford, Mass.; or Valco Instruments Company Incorporated, Houston, Tex.
Each manufacturer's fittings have some conventional features in common, such as a 10-32 UNF internally threaded port. Each port also includes a beveled sealing surface. When a conventional pre-column filter is assembled to one of these fittings, a ferrule on the pre-column filter assembly seals against the inlet port sealing surface, and an externally threaded nut on the pre-column filter assembly engages with the internally threaded inlet port.
However, each component manufacturers' fittings are differently configured in other respects. For example, the longitudinal length of the beveled sealing surface of the inlet port fitting varies from manufacturer to manufacturer. Also, the length of pre-column filter tubing projecting beyond the ferrule on the pre-column filter that is accommodated within the inlet port varies from manufacturer to manufacturer. However, it is important to have the end of the pre-column filter tubing fully inserted into the inlet port of the instrument fitting regardless of the type of fitting utilized. This is to eliminate any significant dead volume within the mated fittings that would tend to slow the passage of analyte through the fitting assembly, resulting in attenuated retention time peaks. In order to accommodate different manufacturer's fittings, each pre-column filter assembly must often be differently constructed so that a corresponding length of tubing projects beyond the ferrule on the filter assembly.